1. Field of the Invention
The invention relates to accessories for use with a conventional rotary lawn mower, the accessories providing three distinct operations, namely grass cutting, grass mulching and power raking.
2. Prior Art
A conventional lawn mower has a bar provided with two oppositely disposed cutting edges which cut the grass as the bar is rotated and the mower is passed over the grass. When the cutting edges become blunt, the bar is removed from the mower, sometimes with great difficulty, and can then be sharpened to permit further use. During this sharpening it is not unusual for dissimilar amounts of metal to be removed from opposite ends of the bar, resulting in an unbalanced bar. This produces undesirable vibrations and can cause premature wear or damage to the lawn mower. Because the bar is secured to the end of the lawn mower output shaft with a heavy bolt, sometimes difficulty can be experienced in loosening this bolt to permit replacement or sharpening of the bar. Also, common bars are often flat and trailing portions of the cutting edges are within the same plane as the cutting edges, and thus drag on the recently cut grass. This increases resistance to rotation of the bar, thus absorbing unnecessary horsepower.
The problem of sharpening the conventional bars of lawn mowers has been appreciated, and disposable blades or cutting elements have been attached to ends of a modified bar, using various means. Examples of replaceable cutting elements for lawn mowers are found in U.S. Pat. Nos. 2,527,472 (Wolf); 2,576,884 (Leigh;) 2,786,322 (McEvers); 2,932,147 (Beeston Jr.); 3,140,575 (Ott et al) and 3,949,541 (Henry). Some of these blades have trailing portions which similarly drag on the grass, thus increasing power consumed. Some embodiments have relatively complex means for securing the blade to the end of the bar, and also require removal of the bar from the mower to permit replacement. This bar removal can of course be difficult due to the heavy bolt required to secure the bar to the output shaft of the mower. Other blades are relatively complex, and are designed to be sharpened many times in view of the relatively high cost of producing them, with a corresponding risk of uneven sharpening, resulting in unbalance of the bar. To simplify attaching the blade to the bar, some references show simple but non-positive attachments wherein a spring force, interference, or centrifugal force is required to hold the cutting element on the end of the bar. While this might be adequate while the cutting element is new, or if the lawn to be cut is very level and free of stones, but such types of non-positive attachment can be a problem if the cutting element becomes old and worn, or loosened, or if the mower hits a rock whilst cutting. In these instances, the element can be dislodged accidently and thrown from the mower, with subsequent risk of injury to persons nearby.
If a lawn has exceptionally long grass, or if the cut grass is required to be left to "mulch" on the lawn, it is usual to set the mower to a relatively high cutting height, and to cut the lawn at that particular height. The lawn mower blade height can then be adjusted to a lower setting, and the mower can then once again pass over the lawn, cutting the grass sequentially and progressively lower with each adjustment. With this type of sequential cutting, in which the height of the cutting bar is progressively lowered relative to the lawn, the grass that had been previously cut is usually cut once again, concurrently with the grass remaining in the lawn. However, with exceptionally long grass the build up of cuttings on the lawn can overload the lawn mower, causing frequent stalling. Also, the grass cut in this manner usually is not cut very finely and is often unevenly dispersed on the lawn, producing unsightly winrows. Uneven dispersion of grass cuttings on the lawn does not produce the best type of mulching conditions, and commonly the lawn requires raking after such cutting. Specialized "mulching blades" are available which permit mulching of long grass in one pass and at one setting of the law mower, but these blades require removal for sharpening, with a subsequent risk of becoming unbalanced.
It is known to provide a bar for a lawn mower which has a rack attachment at each end. Such a bar is available to power rake the lawn, but the conventional cutter bar requires removal, and the power rake bar substituted. As stated previously, difficulty can be encountered when removing the heavy bolt that secures the bar to the output shaft. Also, such bars do not have an integral fine adjustment means for adjusting height of the power rake attachment, which is quite critical when raking well groomed lawns. Instead, the prior art raking bar relies on the height adjustment for the mower itself, which might be too coarse.